1. Field of the Invention
The present invention relates to a laser processing apparatus for performing laser processing to a workpiece by applying a pulsed laser beam thereto.
2. Description of the Related Art
In a semiconductor device fabrication process, a plurality of crossing division lines called streets are formed on the front side of a substantially disk-shaped semiconductor wafer to thereby partition a plurality of regions where a plurality of devices such as ICs and LSIs are respectively formed. The semiconductor wafer is cut along the streets to thereby divide the regions where the devices are formed from each other, thus obtaining a plurality of individual semiconductor chips. Further, an optical device wafer is provided by forming a plurality of optical devices including photodetectors such as photodiodes and light emitting devices such as laser diodes on the front side of a sapphire substrate. The optical device wafer is also cut along the streets to obtain the individual optical devices divided from each other, such as photodiodes and laser diodes, which are widely used in electric equipment.
As a method of dividing a wafer such as a semiconductor wafer and an optical device wafer along the streets, there has been proposed a method including the steps of applying a laser beam to the wafer along the streets to thereby form laser processed grooves on the wafer or modified layers inside the wafer and next breaking the wafer along the laser processed grooves or the modified layers. Such laser processing is performed by using a laser processing apparatus including a chuck table for holding a workpiece and laser beam applying means for applying a laser beam to the workpiece held on the chuck table. The laser beam applying means is composed of a laser oscillator for oscillating a laser beam, focusing means for focusing the laser beam oscillated by the laser oscillator onto the workpiece held on the chuck table, and optical transmitting means for guiding the laser beam oscillated by the laser oscillator to the focusing means.
In general, the optical transmitting means for guiding the laser beam oscillated by the laser oscillator to the focusing means is provided by an optical system composed of a lens and a mirror. However, there is a problem such that the optical system composed of the lens and the mirror mentioned above has a low degree of design flexibility depending on its location. To solve such a problem, optical transmitting means using an optical fiber has been proposed (see Japanese Patent Laid-open No. 2007-207856, for example).